Production of metal powders



Aug. 5, E958 L. SCHLECHT ETAL PRODUCIION OF METAL POWDERS Filed Des. 29, -1954 INVI:NTORS: LEO SCHLECHT ERNST OESTREICHER United States Patent ders With uniform particle size from metal carbonyls.

In the production of metal powders by thermal decom position of metal carbonyls in a heated free space it is desirable to obtain a metal powder of which the particle size is uniform and which exhibits a minimum of agglomeration of primary particles to secondary, larger agglomerates. Especially in the processing of metal powders, as for example nickel powder, With very W bulk densities to porous accumulator electrodes, the presence of a considerable proportion of coarse spongy agglomerates, in addition to very fine particles, is detrimental to the properties of the eleetrodes. These agglomerates prevent the formation of a uniform pore Width in the electrode, thereby increase the electrical resistance in the interior of the electrode and reduce the capacity constancy of the accumulator.

The spongy agglomerates pxesent in the powder are also troublesome in other purposes of employment, and in sorne cases this is attributable to the fact that they have a higher carbon and oxygen content than the finer particles 0f the powder.- This difference in the purity of the various particles of powder is a considerable drawback in working up the powder by powder-metallurgical methods, for exarnple in the produetion of sintered permanent magnets.

We have now found that the formation of such agglomerates in the production of metal powders, in particular nickel, iron or iron-nickel powders for the produetion 02 porous electrodes for alkaline accumulators, by thermal decomposition of metal carbonyls in the free space of an externally heated container can be substantially prevented by keeping those surfaces of the Wall of the container which do not serve for the supply of the heat necessary for the decomposition, at a temperature which lies at or slightly above the eondensation temperature of the metal carbonyl to be decomposed.

The industrial operation of this process is effected in general by a cooling of that part of the decomposer through which the heat necessary for the decomposition is not supplied, and which without cooling would acquire an undesirably high temperature by radiation or heat conduction. In particular the upper part of the decomposer, where the carbonyl is introduced and which is preferably constructed as a conical cover, is cooled 'by a c00ling means, as for example by a cooling jacket o1 a cooling coil, to that temperature at which a conclensation of the introduced metal carbonyl can still not take place but at which on the other band any considerable decomposition of the metal carbonyl is no longer possible.

As the cooling medium for the said places of the decomposer it is preferable to use wa-ter or steam, and the cooling effect can be adjusted to the desired degree by means of the speed of flow cf the cooling medium chosen.

The spatial extent of the cooling is preferably of such dimensions that the cooling action extends up to that part of the decomposer which is externally heated. In

' 2,846299 Patented Aug. 5, 1958 2 this way there is obtained a rapid transition from the low temperature produced by cooling to the high decomposer Wall temperature eflected by the external beating. The shorter this transition from 10W to high temperature, the better is the reduction in the formation of coarse agglomerates at this point. It is also preferable so as to construct the decomposer and the c'ooling means that the transi-tion from 10W to high temperature takes place Where the decomposer has the greatest internal width. It is simplest to choose a cylindrical tube as the decomposer, which is provided at the top With a" conical lid which is cooled down to the point at which it is mounted 011 the tube.

The temperature to which cooling is effected is dependent on the boiling point of the metal carbonyl to be decomposed. Generally speaking the cooling is to the greatest possible extent but not to such an extent that a condensation -of the metal carbonyl vapor can take place because otherwise liquid carbonyl in the form of drops will fall through the heated free space and thereby contaminate the powder and render it inflammable and moreover cause the formation of coarse floeculent metal particles. In the decomposition of undiluted iron carbonyl, it is suitable in general to maintain a temperature of about 110 C. in the neighbourhood of the entry of the carbonyl into the decomposer, and this can be el1eeted by using as cooling medium a current of steam of c-orresp0nding temperature. In the case of undiluted nickel carbonyl vapor it is preferable to cool to a temperature lyingimmediately above the boiling point of the nickel carbonyl, for example to 60 C. to C. When working with carbonyl vapor which is diluted with gases, as for example arnmonia 01' carbon monoxide, the temperature necessary according to this invention may lie lower than the boiling temperature of the carbonyl in question because the condensation of the carbonyl vapor takes place only at lower temperatures corresponding to the vapor tension which is reduced by the presence of the diluent gases.

If it is desired to produce a specially light nickel pow der, it is advantageous to raise the temperature of the decomposer Wall which adjoins the cooled surface 'to* such an extent that this temperature lies at least 270 C. higher than the temperature in the middle of the free space.

In rarer cases it may be necessary to carry out a beating instead of the above-described cooling, namely when spots having too 10W a temperature can occur in the decomposer when they are too far away from the heat source. By heating these spots to just above the sondensation temperature of the carbonyl, the formation of coarse agglomerates can be precluded also in such cases.

The regulation of temperature according to this invention is advantageous irrespective cf whether the decomposition of the metal carbonyl is carried out at atmospheric; reduced 01' increased pressure and with or without dilution with gases or vapors. v

Especially when it is desired to produce metal powder with a very 1ow bulk densit there is bbtained by the present process a considerable' simplification and a considerable increase in the yield of uniformly composed light powder which is very Well suited for the production of porous electrodes for alkaline accumu-" lators which are to have a practically invatiable capacity.

A further advantage of the process according to this powder is produced; the decomposer becomes clogged in Example Into -Container A, of which the upper {zart is heated by a heating jacket B to an internal temperature cf about 230 C., vaporous nickel carbonyl is led continuously from a vaporizer C through a pipe D. The carbonyl vapor enters at the middle of a com'cal, doubIe-walled 1id E which closes the top of the container A. Water at a temperature of 60 C. enters the hollow space of the lid Ethrough inlets F ancl F and leaves through an outlet G at a temperature of 80 C. In the same way the lower part of the container A is also preferably kept at a temperature between 60 C. and 80 C., an inlet F and an outlet G for the supply and withdrawal of water being provided. Hut gases at a temperature of 550 C. are introdnced through a pipe H into the heating jacket B in such a quantity that a temperature of about 220 C. in the central part of the container A is maintained. The heating gas leaves the jacket B through an outlet I. The nickel powder formed by the decomposition of the carbonyl and collecting in the lower part of the coutainer A is removed periodically by means of a sluice K. The carbon monoxide formed by the decomposition leaves the container A through a pipe L and is freed in the usual way by a filte1 device M from the residual nickel powder which is removed from the filter device throngh a pipe N.

The particles of the resulting nickel powder, Which has a carbon content of 0.09%, are, in spite of the 10W bulk density cf 0.5 kilogram per lit1e, so small and free from agglomerates that upon sieving through a sieve with 16900 meshes per square centimetre practically no residue remains.

011 the contrary by operating in the same decomposer without the above mentioned cooling of the lid, it is true that a nickel powder with the same bulk density is obtained, b11t'it contains large agglomerates of upto 3 millimetres which have a carbon content of 0.21% as compared with a carbon content of about 0.10% in the finer Particles. When this nickel powder is sieved, only 75% Passes through a sieve With 16900 meshes per square centimetre. If the large agglomerates are removed by mechanical comminution, the yield of fine particles can be increased frorn 75% to 95%, but the bulk density is thereby increased to 0.8 kilogram per litre and the car bon content of the powder which has passed through the sieve is also increased from 0.10 to 0.15%. This sieved nickel powder has therefore become heavier and less pure and is therefore less suited for use for m'any purposes, in particular for powder-metallurgical purposes, as :for example for the production of porous electrodes.

The process according to the present invention thus not only gives considerably better yields of a more uniform powder without coarse agglornerates, but also a powder with lower bulk density and higher purity than the decomposition of carbonyl without such a temperature regulation.

What we claim is:

1. In a process for the production of a metal powder by therrnal decornposition of a meta1 carbony1 in the free space of a container having the heat of decomposition app1ied externally through the walls thereof, the improvement which comprises maintaining the inner Wall surfaces of the container not uti1ized for supplying heat for decomposition at a temperature in the vicinity f but above the condensation temperature of the metal carbony1.

2. In a process for the production of nickel powder by therrnal decomposition of nickel carbonyl in the free space of a container having the heat of decomposition applied externally through the walls thereof, the improvernent which comprises maintaining the inner wall surfaces of the container not utilized for supplying heat for decomposition at a temperature in the vicinity of but above the condensation temperature of the nic'kel carbonyl.

3. In aprocess for the production 0f iron powder by thermal decomposition of iron carbonyl in the free space of a container having the heat 01 decornposition applied externally through the Walls thereof, the improvement which comprises maintaining the inner Wall surfaces of the container not utilized for supplying heat for decomposition at a temperature in the vicinity of but above the condensation temperature of the iron carbonyl.

4. In a process for the production of nickel-iron powder by thermal decornposition of a mixture of nickel carbony1' and iron carbonyl in the free space of a container having the heat 'of decomposition applied externally through the Walls thereof, the improvement which comprises maintaining the inner Wall surfaces of the container not utilized for supplying 'heat for decomposition at a temperature in the vicinity of but above the coudensation temperatre of the mixture of nickel carbonyl and iron carbonyl.

5. In a process for the production of nickel powder by thermal decornposition of nickel carbonyl in the free space of a container having the heat of decomposition applied externally through the walls thereof, the improvement which comprises maintaining the inner Wall surfaces of the container not utilized for supplying heat for decomposition at a temperature of 60 C. to C.

6. In a process for the production of iron powder by thermal decomposition of iron carbonyl in the free space of a container having the heat of decornposition applied externally through the Walls thereof, the improvement which cornprises maintaining the inner Wall surfaces of the container not utilized for supplying heat for decomposition at a temperature of about C.

7. In a process for the production of nickel powder by thermal decornposition of nickel carbonyl in the free space of a container having the heat of decornposition applied externally through the Walls thereof, the improvement which comprises maintaining the inner Wall surfaces utilized for supplying heat for decomposition at a temperature of at least 270 C. higher than that temperature in the middle of the free space, and maintaining the adjacent inner Wall surfaces of the container not utilized for supplying heat for decomposition at a temperature of 60 C. to 80 C.

8. In an apparatus for the production of a metal powder by thermal decomposition of a metal carbonyl said apparatus being of the type having a closed elongated comtainer, an inlet for carbonyl vapor, an outlet for metal powder formed in the decornposition, an outlet for carbon monoxide formed in the decornposition, and means for externally applying heat through a portion of the Walls of the container to supply the heat of decomposition; the improvement in cornbination with said apparatus which comprises means for rnaintaining the inner wall surfaces 0fthe container not utilized for supplying heat for decornposition at a temper-ature in the vicinity of but above the condensation temperature of the met-al carbonyl.

9. In an apparatus for the production of a metal powder by thermal decornposition of a n1etal carbonyl, said apparatus being of the type having a vertically-arranged elongated container including a bottom and side Walls, a cover enclosing the Container at its upper end, an inlet for earbonyl vapor in the cover, an outlet at the bottorn cf the container for metal powder formed in the decomposition, an outlet near the bottom of the container for catbon monoxide formed in the decomposition, and means for externally applying heat through at least a portion 5 of said side Walls of the container to supply the heat of decomposition; the improvernent in combination With said apparatus which comprises cooling means in said cover for maintaining the inner Wall surface of said cover at a temperature in the vicinity of but above the condensation temperature cf the metal carbonyl.

10. An apparatus as defined in :claim 9 wherein the inner wall surfaces forming a lower portion of the comtainer in the vicinity of the outlets for meta1 powder and carbon monoxide and nog utilized for supplying heat for decomposition are =also provided with cooling means for maintaining said inner Wall surfaces at a temperature in the vicinity cf but above the condensation temperature of the metal carbonyl.

11, An apparatus as defined in c1aim 9 wherein the cover is a hollow cone having its base adjacent to the side 6 Walls cf the container through which the hat of decornposition is applied externally and its apex provided With an opening for the introduction of carbonyl vapor, said hollow cone formed Wi(h an outer Wall spaced from {an inner Wall for circulation cf a cooling medium between said unter Wall and said inner Wall.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR THE PRODUCTION OF A METAL POWDER BY THERMAL DECOMPOSITION OF A METAL CARBONYL IN THE FREE SPACE OF A CONTAINER HAVING THE HEAT OF DECOMPOSITION APPLIED EXTERNALLY THROUGH THE WALLS THEREOF, THE IMPROVEMENT WHICH COMPRISES MAINTAINING THE INNER WALL SURFACES OF THE CONTAINER NOT UTILIZED FOR SUPPLYING HEAT FOR DECOMPOSITION AT A TEMPERATURE IN THE VICINITY OF BUT 